In general, according to the prior art the surface of a compound semiconductor substrate for epitaxial growth is polished into a mirror finished surface. The roughness of this surface is generally less than 1 .mu.m as measured over each 1 mm line. Such a substrate having a mirror finished surface or a nearly mirror finished surface is obtained by slicing a single-crystalline ingot, thereafter rounding the as-obtained substrate as needed, lapping its surface, and polishing the same as needed. It has been common knowledge for those skilled in the art to finish the surface of such a substrate into a mirror finished surface or nearly mirror finished surface, in order to maintain important characteristics, such as flatness, uniformity in thickness and stability of electro-optical properties, of an epitaxial layer that is to be grown on the surface of the substrate.
While epitaxial growth is carried out by various methods such as vapor deposition, liquid phase epitaxy and molecular beam epitaxy, a substrate having a mirror finished surface or a surface which is nearly mirror finished is generally employed in every method. In fact, it can be said that there has been no idea of using a substrate having a rough surface to make a liquid phase epitaxial wafer for a light emitting diode.
Manufacturing such a conventional substrate having a mirror finished surface or a surface which is nearly mirror finished, however, requires much time and trouble as well as a high cost, due to the required slicing, lapping and polishing steps. Further, a GaAs substrate about 76 mm in diameter and 600 .mu.m in thickness weighs about 14 g, and easily slips from holding tools and falls down during transportation if the substrate has a mirror finished surface.